The present invention relates to a dot recording apparatus for serial printers and the like, and more particularly, to a dot recording apparatus using a dot recording head for recording characters on a recording medium carried on medium regulators which are disposed opposite to the recording head and extending separately from each other in the main scanning direction.
A related dot recording apparatus for an ink-jet printer will be described. A recording head has a plurality of dot forming elements for forming a nozzle row on a head face. The dot forming elements is lined up with a substantially fixed pitch along a subscanning direction, and driven during main scanning to record characters on a recording medium. A plurality of medium regulators is disposed opposite to the head face of the recording head and separated from each other in the main scanning direction. The distance between the recording medium and the dot forming elements is defined by the top faces of the respective medium regulators. A feeding roller is disposed closed to the upstream side of the recording head and formed with a feeding drive roller and driven feeding rollers in combination so as to feed the recording medium toward the recording head while nipping the recording medium therein between. A discharging roller is disposed close to the downstream side of the recording head and used for discharging the recording medium downstream.
Further, the feeding roller is formed with the feeding drive roller having a substantially uniform diameter in the longitudinal main scanning direction and a plurality of driven feeding rollers arranged with a fixed pitch in the main scanning direction. The nipping pressure applied to the recording medium onto the feeding roller is generated by pressing each of the driven feeding rollers against the feeding drive roller by means of the force of springs. Moreover, the discharging roller is formed with discharging drive rollers and driven discharging rollers.
In addition to defining the distance between the recording medium and the dot forming elements, the medium regulators guides valley portions of undulating deformation of a recording medium based on cockling to the space between the medium regulators separated from each other. The cockling is an undulating deformation phenomenon resulting from the elongation of paper as a recording medium that has absorbed ink. In other words, the role of the medium regulators also includes preventing the paper from being brought into contact with the head face and consequently stained with ink as the paper swells toward the recording head face due to the undulating deformation of the paper based on the cockling.
Nevertheless, in spite of the fact that the medium regulators have heretofore been disposed with a predetermined pitch in the main scanning direction, no consideration has been given to the relative position of the driven feeding rollers pressed by the feeding drive roller under the nipping pressure. More specifically, no regulated relation of arrangement has existed between the medium regulators and the driven feeding rollers, and both of them have been disposed in mutually unconnected relative positions.
Therefore, even though the medium regulators are disposed with the predetermined pitch in the main scanning direction together with the formation of a base of cockling between the medium regulators, a cockling interval in the case of cockling of paper has become unstable and there has been a case where the cockling interval voluntarily varies at an integer multiple of the pitch of the medium regulator. When a great cockling interval is produced, the amplitude (height of the cockling) also grows larger and there has been the fear of causing the paper to be stained as it contacts the recording head.
With the structure of pressing paper against the medium regulators by the feeding roller together with the structure of holding down the paper by the driven discharging rollers, it has heretofore been arranged to stabilize the cockling interval, that is, to prevent the paper from greatly swelling toward the recording head face. In the case of a multiple band head, for example, the distance between the feeding roller and the driven discharging rollers becomes greater as the length of the nozzle row increases. The problem in this case is that the effect of stabilizing the cockling interval becomes unsatisfactory and the paper tends to be easily stained.
An object of the present invention is to provide a dot recording apparatus designed to stabilize a cockling interval to ensure that the fear of staining paper with ink as paper swells toward a recording head face due to cockling is decreased.
In order to achieve the above object, according to the present invention, there is provided a dot recording apparatus, comprising:
a recording head, having a head face on which at least one row of dot forming elements which form dots on a recording medium is arranged in a subscanning direction thereof;
a drive feeding roller, extending in a main scanning direction of the recording head;
a plurality of driven feeding rollers, arranged in the main scanning direction with a predetermined interval, such that the recording medium is nipped between the drive feeding roller and the driven feeding rollers to be fed to the recording head; and
a plurality of medium regulators, arranged in the main scanning direction with a predetermined interval which is associated with the arrangement of the driven feeding rollers, the medium regulators being opposed to the head face such that top faces of the medium regulators define a distance between the recording medium carried thereon and the head face.
In this configuration, the cockling interval of the paper can be made to substantially coincide with the interval of the relevant medium regulator by the nipping force of the feeding rollers and the relevant medium regulator supporting from below the paper affected by the nipping force. Thus the cockling interval becomes stabilized to suppress the probability of staining the paper with ink due to the swelling of the paper toward the recording head face because of cockling.
Preferably, each of the medium regulators extend in the subscanning direction such that the top faces extend beyond an upstream end of the dot row of the dot forming elements.
In this configuration, it is possible to force the recording medium to cockle as desired before the medium is wetted with ink. Therefore, when ink is landed on the medium to be cockled, the medium has been already cockled in the desired interval which has been predetermined by the medium regulators, so that the cockling interval is further stabilized.
Preferably, the predetermined interval of the medium regulator is 20 mm or more. Although the cockling is hardly produced with an interval less than 20 mm in almost all kinds of paper, setting of the interval between the adjoining medium regulators at 20 mm or greater makes it possible to smoothly generate cockling with the desired cockling interval.
Preferably, the dot recording apparatus further comprises a subregulator, disposed between the respective adjacent medium regulators at an area opposed to a downstream side of the head face to support the recording medium together with the medium regulators.
In this configuration, the force of supporting from below the paper by the relevant subregulators affects the area of the medium regulators positioned further upstream, and this results in decreasing the depth of cockling in the cockling interval forcibly provided. Therefore, the variation of the paper gap in the base portion of cockling can be kept in a smaller range.
Here, it is preferable that a top face of the subregulator is not higher than the top face of the medium regulator. In this configuration, the influence of the primary function of the medium regulators which forces the medium to cockle with a predetermined interval is lowered.
Preferably, the dot recording apparatus further comprises a plurality of discharging roller pairs for discharging the recording medium on which dots are recorded by the recording head. Here, each of the discharging roller pairs and the associated medium regulator are situated on the same line which extends in the subscanning direction. In this configuration, the cockling interval can be further stabilized.
Preferably, two adjacent driven feeding rollers are connected with a shaft which extends in the main scanning direction to form a driven feeding roller unit. Here, each of the medium regulators and a center portion in the main scanning direction of the shaft in each of the driven feeding roller units are situated on the same line which extends in the subscanning direction.
In this configuration, the cockling interval can be stabilized in accordance with the predetermined regularity.
Alternatively, each of the medium regulators and a center portion in the main scanning direction of the associated driven feeding roller are situated on the same line which extends in the subscanning direction.
Still alternatively, each of the medium regulators and a center portion in the main scanning direction of every other driven feeding roller are situated on the same line which extends in the subscanning direction.
In this configuration, the cockling interval can be stabilized in accordance with the predetermined regularity.
Still alternatively, each of the medium regulators and a portion of the associated driven feeding roller, which is shifted from the center portion of the associated driven feeding roller in the main scanning direction, are situated on the same line which extends in the subscanning direction.
In this configuration, the cockling interval can be stabilized in accordance with the predetermined regularity.
Still alternatively, two adjacent driven feeding rollers are connected with a shaft which extends in the main scanning direction to form a driven feeding roller unit. Here, each of the medium regulators and an associated portion between the adjacent driven feeding roller units are situated on the same line which extends in the subscanning direction.
In this configuration, the cockling interval can be stabilized in accordance with the predetermined regularity.
Preferably, the outermost medium regulator is disposed such that a side edge of the recording medium is placed on a substantially center portion in the main scanning direction of the top face thereof.
In this configuration, since a range of forcibly flattening the edge portion of the medium is shortened, a cockling shape similar to that of a mountain portion formed by the medium regulator can be formed on the outermost medium regulator. Namely, the cockling shape can be uniformized over the whole width length of the medium.